Launch the Google Home app on your mobile device, and you should see a free $25 Walmart credit.
It
looks like this.
Press "redeem offer" to add the credit to your Google Express account.

Go to Express.Google.com, click on Walmart, shop for $25 worth of items, and have them delivered for free with no shipping costs.

Your $25 credit expires January 31.
The Google Home Mini normally sells for $49.
You can redeem this deal twice per household, if you want two Google Home Minis.
Limit one coupon per Google Express order.
So, if your Google Express shows another promotion, like $15 off your first $55 order, you cannot combine that promo with your $25 credit.
Google Home is a direct competitor of Amazon Echo.
Both can set timers, look things up, and tell you news & weather.
We recommend Google Home for someone who uses a Chromecast and wants voice control, someone who wants voice control of their Nest thermostat or smart light switches, or wants to hear their Google Calendar.
Google Home also plays music through Spotify, Pandora, Google Play Music, or a YouTube Red ($10/mo) account.
Google Home can also distinguish between multiple people's voices in the house, each with their own Google accounts.Can you do this deal twice?

According to the terms on the bottom of their page, "two coupons total per household."
So, your home can get two Google Home Minis and two $25 shopping credits.

Can you gift the Google Home Mini and Keep the $25 Credit?

No.
The person who links the Walmart-purchased Google Home Mini to their Google account will get the $25 credit.